Some people forgot marking feature even existed in this game (I'm one of them) and on JP side they started a thread to make a better use for it where you can use outside of leve/content. Here's reps response to this one.

Quote Originally Posted by Mocchi View Post
こんばんは。
Good evening,

現行版では他に優先事項があるため、現状、マーキング機能を改修する予定はありません。
There are higher priority tasks for the current version so we have no plans for modifying marking feature.

新生では、マーキング機能は一から作り直します。
詳細な仕様は決まっていない部分もありますが
In 2.0 we will rebuild the marking feature from scratch,
The details are not decided completely but
  • マーカーとサインの統合
    combine marker and sign (I don't get what they mean by sign)
  • 1キャラに対して複数のマーキングを可能に
    Be able to add multiple markers in 1 character
  • 現在のリーヴ／コンテンツ縛りを撤廃
    Get rid of being excluded where it can be used in leave/content only

など、現状使いにくくなっている部分が大幅に改善されます。
We will modify largely to improve the feature which is making it hard to use.